A cleanroom is a controlled environment where products are manufactured. It is a room in which the concentration of airborne particles is controlled to specified limits. Eliminating sub-micron airborne contamination is really a process of control. These contaminants are generated by people, process, facilities and equipment. They must be continually removed from the air. The level to which these particles need to be removed depends upon the standards required. The most frequently used standard is the Federal Standard 209E. The 209E is a document that establishes standard classes of air cleanliness for airborne particulate levels in cleanrooms and clean zones. Strict rules and procedures are followed to prevent contamination of the product.
The following table shows the latest cleanroom classifications. Note that ISO Class 2 is equivalent to 209 Class 10.
TABLE 1Airborne Particulate Cleanliness ClassesClassificationMaximum concentration limits (particles/m3 of air)numbersfor particles equal to and larger than the sizes listed belownumbers (N)0.1 micron0.2 micron0.3 micron0.5 micron1 micron5 micronISO 1102ISO 210024104ISO 31,000237102358ISO 41042,3701,02035283ISO 510523,70010,2003,52083229ISO 6106237,000102,00035,2008,320293ISO 7352,00083,2002,930ISO 83,520,000832,00029,300ISO 935,200,0008,320,000293,000
The only way to control contamination is to control the total environment. Air flow rates and direction, pressurization, temperature, humidity and specialized filtration all need to be tightly controlled. The sources of these particles also need to controlled or eliminated whenever possible. Cleanrooms are planned and manufactured using strict protocol and methods. They are frequently found in electronics, pharmaceutical, biopharmaceutical, medical device industries and other critical manufacturing environments.
It only takes a quick monitor of the air in a cleanroom compared to a typical office building to see the difference. Typical office building air contains from 500,000 to 1,000,000 particles (0.5 microns or larger) per cubic foot of air. A Class 100 cleanroom is designed to never allow more than 100 particles (0.5 microns or larger) per cubic foot of air. Class 1000 and Class 10,000 cleanrooms are designed to limit particles to 1000 and 10,000 respectively.
A human hair is about 75-100 microns in diameter. A particle 200 times smaller (0.5 micron) than the human hair can cause major disaster in a cleanroom. Contamination can lead to expensive downtime and increased production costs. Once a cleanroom is built, it must be maintained and cleaned to the same high standards.
Contamination is a process or act that causes materials or surfaces to be soiled with contaminating substances. There are two broad categories of surface contaminants: film type and particulates. These contaminants can produce a “killer defect” in a miniature circuit. Film contaminants of only 10 nm (nanometers) can drastically reduce coating adhesion on a wafer or chip. It is widely accepted that particles of 0.5 microns or larger are the target. However, some industries are now targeting smaller particles.
A partial list of contaminants is provided below. Any of these can be the source for killing a circuit. Preventing these contaminants from entering the cleanroom environment is a major objective. It has been found that many of these contaminants are generated from five basic sources: facilities, people, tools, fluids and the product being manufactured.
1. Facilities: Walls, floors and ceilings; Paint and coatings; Construction material (sheet rock, saw dust etc.); Air conditioning debris; Room air and vapors; Spills and leaks
2. People: Skin flakes and oil; Cosmetics and perfume; Spittle; Clothing debris (lint, fibers etc.); Hair
3. Tool Generated: Friction and wear particles; Lubricants and emissions; Vibrations; Brooms, mops and dusters
4. Fluids: Particulates floating in air; Bacteria, organics and moisture; Floor finishes or coatings; Cleaning chemicals; Plasticizers (outgasses); Deionized water
5. Product generated: Silicon chips; Quartz flakes; Cleanroom debris;
Aluminum Particles
Current methods and devices used to decrease contamination include HEPA (High Efficiency Particulate Air) filters. These filters are extremely important for maintaining contamination control. They filter particles as small as 0.3 microns with a 99.97% minimum particle-collective efficiency. Cleanrooms are designed to achieve and maintain an airflow in which essentially the entire body of air within a confined area moves with uniform velocity along parallel flow lines. This air flow is called laminar flow. The more restriction of air flow the more turbulence. Turbulence can cause particle movement. In addition to the HEPA filters commonly used in cleanrooms, there are a number of other filtration mechanisms used to remove particles from gases and liquids. These filters are essential for providing effective contamination control. Cleaning is also an essential element of contamination control. The requirements for cleanroom garments will vary from location to location. Gloves, face masks and head covers are standard in nearly every cleanroom environment. Smocks are being used more and more. Jump suits are required in very clean environments. Care must be taken when selecting and using commodity items in cleanrooms. Wipers, cleanroom paper and pencils and other supplies that service the cleanroom should be carefully screened and selected. Review of the local cleanroom requirements for approving and taking these items into the cleanroom is essential. In fact, many cleanroom managers will have approval lists of these types of items.
There are both physical and psychological concerns when humans are present in cleanrooms. Physical behavior like fast motion and horseplay can increase contamination. Psychological concerns like room temperature, humidity, claustrophobia, odors and workplace attitude are important. Ways people produce contamination include body regenerative processes resulting in skin flakes, oils, perspiration and hair; behavior including the rate of movement, sneezing and coughing; attitude in the work habits and communication between workers. People are a major source of contamination in the cleanroom, as demonstrated below in table 2. Table 2 lists a person's typical activities and the corresponding rate or particle production (number of particles produced per minute). The particles are 0.3 microns and larger.
TABLE 2Typical activities and rate of particle productionRate of Particle (0.3 micronsand larger) ProductionPeople Activity(particles/minute)Motionless (Standing or Seated)100,000Walking about 2 mph5,000,000Walking about 3.5 mph7,000,000Walking about 5 mph10,000,000Horseplay100,000,000
It is an object of the present invention to provide a device and methods for use in decreasing contamination in environments such as cleanrooms.
It is further an object of the present invention to provide a method for decreasing or limiting the airborne transmission of viruses and bacteria in environments such as cleanrooms.
It is yet a further object of this invention to manufacture a device for the measurement of exhaled particle number and particle size to determine if a formulation for decreasing particle exhalation is needed.
It is an object of the present invention to provide a method for using a device for the measurement of exhaled particles by individuals.